Key Points of the Thesis

• Understanding the dynamics of coarse sediments in complex bed configurations (surface arrangement, bedform, and clogging).
• Highlighting the role of different topographic scales of the bed in sediment transport.
• Proposed tools for estimating sediment transport: phenomenological model, recommendations, and a sediment transport formula incorporating the effect of bed stability.

Abstract

This PhD thesis aims to understand gravel dynamics in Alpine rivers at low bed shear stress using laboratory experiments. Alpine river beds are often poorly sorted and composed of sediments ranging from clay to pebble. To understand interactions between these classes is an issue for predicting bedload rate. Laboratory experiments were performed in a 18m long and 1m wide flume, under unsteady flows. Two types of bed were investigated: unimodal and bimodal beds. A particular attention was paid to the bed construction, which was conducted in order to obtain a nature-like bed 12with different bed arrangements and degrees of clogging. Unimodal beds were made of moderately sorted gravels with different bed surface arrangements. Bimodal beds were made of moderately sorted gravels in which fine sediments (sand or silt) were infiltrated. Gravel rate was found to be impacted by the bed arrangement degree, the fine sediment concentration within the bedload layer and the changes in bed properties due to fine sediment presence (bed cohesion, bed permeability). The more packed the bed is; the more difficult it is to move gravels. The more concentrated in fine sediment the bedload layer is; the easier the transport of gravels is. The shape of fine sediments can also be an important factor for modifying the gravel rate. The presence of cohesive fine sediments within the bed matrix reduces significantly the gravel rate. A conceptual model was developed to recap the different processes controlling gravel transport. It provides a phenomenological description of the overall bed responses to a hydrograph. This tool is designed to help understanding, estimating or interpreting gravel transport in Alpine rivers. The conceptual model was discussed and applied to a field case made on the Arc River. Using the model, we also suggest a new dimensionless analysis for the construction of a bedload predicting model involving parameters describing bed arrangement, bed properties and fine sediment presence.

Publications and communications

Articles in Peer-Reviewed International Scientific Journals

• Perret, E., Berni, C., Camenen, B., (2019). How does bed surface impact bedload transport over gravelbed rivers? Submitted in Earth Surface Processes and Landforms.
• Berni, C., Perret, E., Camenen, B., (2018). Characteristic time of sediment transport decrease in static armour formation. Geomorphology, 317, 1-9, doi : 10.1016/j.geomorph.2018.04.004.
• Perret, E., Berni, C., Camenen, B., Herrero, A., El kadi Abderrezzak, K., (2018). Transport of moderately sorted gravel at low bed shear stresses: The role of fine sediment infiltration. Earth Surface Processes and Landforms, 43, 1416-1430, doi : 10.1002/esp.4322.
• Communications dans des congrès internationaux avec actes (papiers scientifiques)
• Perret, E., Berni, C., Camenen, B., (2018). Impact of bed surface arrangement on bedload rate:
• comparisons between loose, armored and water-worked beds. RiverFlow, Lyon, France.
• Perret, E., Berni, C., Herrero, A., Camenen, B., (2016). Laser scanning method to characterize bed
• arrangement and its influence on incipient motion of gravel sediments. RiverFlow, Saint-Louis, USA.
• Perret, E., Herrero, A., Berni, C., El Kadi Abderrezzak, K., Camenen, B., (2015). Incipient motion of
• bimodal mixture of gravel and silt: a laboratory experimental study. 36th IAHR Congress, The Hague,
• Netherlands.

Communications at International Conferences with Proceedings (Extended Abstracts)

• Camenen, B., Herrero, A., Dramais, G. , Thollet, F, Le Bescond, C., Perret, E., Berni, C., (2015). Field experiment on the dynamics of fine sediments over a gravel bar in an alpine gravel-bed river. 9th symposium RCEM, Iquitos, Peru.
• Perret, E., Herrero, A., Berni, C., El kadi Abderrezzak, K., Camenen, B., (2015). Incipient motion of bimodal mixture of gravel and silt: a laboratory experimental study. 9th symposium RCEM, Iquitos, Peru.

Technical Reports

• Camenen, B., Perret, E., Buffet, A., Berni, C., Dramais, G., Thollet, F., Le Bescond, C., Lagouy, M., (2016). Expérience de terrain lors de la chasse de l'Arc (16 juin 2016) pour l'estimation de la dynamique sédimentaire pour des conditions proches du seuil de mise en mouvement des galets. Rapport technique pour EDF, 35 pages.
• Berni, C., Herrero, A., Perret, E., Camenen, B. et Thollet, F., (2015). Décolmatage des sédiments fins dans le lit d'une rivière à graviers. Rapport technique accord agence de l’eau/Irstea.
• Camenen, B., Perret, E., Thollet, F., Buffet, A., Dramais, G., Herrero, A., Berni, C., Le Bescond, C., Lagouy, M., (2015). Expérience de terrain lors de la chasse de l'Arc (9 juin 2015) pour l'estimation de la dynamique sédimentaire pour des conditions proches du seuil de mise en mouvement des galets. Rapport technique pour EDF, 57 pages.

Cite the thesis

Emeline Perret. Transport de graviers à faible contrainte : impact de l'arrangement et de l'infiltration du lit par des sédiments fins. Fluids mechanics [physics.class-ph]. Université de Lyon, 2017. English. ⟨NNT : 2017LYSE1223⟩. ⟨tel-01737702⟩

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